A strap wrench is a tool comprising a flexible strap so attached to a handle that the strap may form a loop. In use, the strap is looped around an object to which torque is to be applied and brought into frictional engagement therewith; the handle is then operated as a lever in order to apply the torque.
Usually, one end of the strap is permanently fastened to the handle whereas the other end can be passed freely through a guide member in order to permit the size of the loop to be continuously adjustable within limits. Prior to use, the loop is closed around the object by taking up the slack by means of the free end of the strap. The handle usually is provided with a working surface adapted to abut a part of the outer surface of the loop. Thus, the strap is gripped, in use, between the said working surface and the object, thereby preventing any loosening of the strap loop.
Small wrenches of this type have been marketed as household gadgets for enabling screw-threaded tops, caps and lids to be readily removed from such containers as bottles and jars. Heavy-duty wrenches of this type are also known; these may utilise a roller chain as the flexible strap (see, for example, U.K. Patent Specification No. 1,222,671).
In the Complete Specification of U.K. Pat. No. 1,347,325 to W. Rutz, there is disclosed a strap wrench wherein the two ends of the strap (which may be a flexible metal strip) extend into the handle. At least one end of the strap is secured to a slide shoe which is mounted on a spindle that is axially immovable, but which can be rotated by means of a grip located on the outside of the handle.
The spindle and slide shoe have complementary screw threads; accordingly, on rotating the spindle by means of the grip, the slide shoe will be moved along the spindle in a desired direction, thereby increasing or decreasing the length of the strap in the loop extending beyond the handle. In this device, the strap is not gripped between the object and a working surface on the handle. Instead, the loop is tightened by rotation of the grip to the desired extent; the slide shoe will then remain fixed, thereby preventing the loop from loosening, until the grip is rotated in the opposite sense.
One disadvantage of the prior-art strap wrenches, however, is that they are difficult or awkward to use on an object whose ends are inaccessible, or accessible only with difficulty, for example, a connector in a long length of piping or conduit. It is usually necessary to remove the free end of the strap from the guide member in the handle and then pass it around the object to be gripped and then back through the said guide member. This is, at best, a cumbersome operation, and may prove extremely difficult for handicapped operators. Moreover, in strap wrenches of the type disclosed by W. Rutz (above), this operation cannot be carried out at all, since both ends of the strap are secured within the handle.
In U.K. Patent Specification No. 388,572 there is disclosed a gripping wrench having two separable members having handle-like portions, which members are secured together by a detachable screw. The wrench is provided with jaws. However, for use with a pipe that is too large to fit within the jaws, a chain is mounted by means of a pin on one of the members, which chain is then passed around the pipe and secured to a hook on the other member. Tension is applied by squeezing together the handle-like portions and is maintained by placing a peg in one of a series of holes in one member; the peg then acts as a stop for the other member. Again, this procedure is rather awkward.